Means for controlling acceleration of a wheel

ABSTRACT

The acceleration of a wheel on a rail vehicle is controlled by using the wheel to drive a generator which produces an electrical signal, the magnitude of which depends on the acceleration of the wheel. This signal is applied to a d.c. control circuit which includes means operable to prevent transmission of driving power to the wheel. The control circuit includes a d.c. source charged by the generator and providing power to the control circuit, and the arrangement also includes a delay network for maintaining the circuit in a condition to prevent transmission of power in the event that the wheels should lock before the power is released.

Clifford et al.

MEANS FOR CONTROLLING ACCELERATION OF A WHEEL Inventors: StanleyClifford, Coventry;

Leonard Ramsay Hiscox, Birmingham, both of England Assignee: GirlingLimited, Birmingham,

England Filed: Mar. 3, 1971 Appl. No.: 120,732

Related US. Application Data Division of Ser. No. 727,469, May 8, 1968,Pat. No, 3,598,452.

Foreign Application Priority Data 1451 Sept. 4, 1973 [56] ReferencesCited UNITED STATES PATENTS 2,918,882 12/1959 Moorhead, Jr. et al.105/61 X 3,564,532 2/1971 Ando 340/262 3,252,022 5/1966 Smith 317/5 XPrimary Examiner-J. D. Miller Assistant ExaminerHarry Ev Moose, Jr.

Attorney-Holman & Stern [57] ABSTRACT The acceleration of a wheel on arail vehicle is controlled by using the wheel to drive a generator whichproduces an electrical signal, the magnitude of which depends on theacceleration of the wheel. This signal is applied to a d.c. controlcircuit which includes means operable to prevent transmission of drivingpower to May 23, 1967 Great Britain .13883/67 Oct 12,1967 Great Bn-tain46582/67 the wheel. The control c1rcu1t 1ncludes a d.c. source Feb. 8,1968 Great Britain ..6223/68 eharged y the generator and Providing P thecontrol circuit, and the arrangement also includes a CL 317/5, 303/21CG, 340/262 delay network for maintaining the circuit in a condition 1m.(:1. G08b 21/00 to Prevent transmission of power in the event that theField of Search 105/61; 303/21 cc; Wheels should leek before the Power sreleased- 317/5; 340/262 1 Claim, 1 Drawing Figure I --T w.w A To- RB ifgins 112; R1? 1113 2k 01 72 15 27 U3 r- R1 R3 u MFA/MW L R12 7 L MEANSFOR CONTROLLING ACCELERATION OF A WHEEL This is a division ofapplication Ser. No. 727,469 filed May 8, 1968, entitled MEANS FORCONTROLLING DECELERATION OF A WHEEL" now US. Patent No. 3,598,452

This invention relates to means for controlling acceleration of a wheel.The invention is particularly, but not exclusively intended for use withrail vehicles.

The invention resides in means for controlling the acceleration of awheel, comprising the generator driven by the wheel, means for producingan electrical signal having a magnitude dependent on the acceleration ofthe wheel, a d.c. control circuit to which said signal is supplied, saidcontrol circuit including means operable in use to prevent transmissionof driving power to said wheel when the magnitude of said signal reachesa predetermined value, a d.c. source which is charged by said generatorand provides power to said control circuit, and a delay network withinsaid control circuit for maintaining the circuit in a condition toprevent supply of power to said wheel in the event that the wheel shouldstart to slip before said power is released.

One example of the invention is illustrated in the accompanying circuitdiagram.

The example to be described relates to brake control means intended foruse on a rail vehicle, where each of the four wheels of the rail vehiclehas associated therewith a self-contained unit for controlling thebraking effort applied to the wheel. Since the arrangement for eachwheel is the same, only one arrangement will be described.

The wheel drives an alternator illustrated diagrammatically at 11, andthe output from the alternator 11 is fed to the input terminals of thefull wave bridge rectifier including diodes D2, D3, D4, D5. The bridgehas output terminals 15, 16, the terminal 15 being connected to a supplyline 14 and the terminal 16 being connected to a supply line 13 throughthe collector and emitter of an N-P-N transistor Q6 having a resistor R8in its emitter circuit. The terminal 16 is further connected to the baseof the transistor 06 through a resistor R12, and the base of thetransistor Q6 is connected to the terminal 15 through a Zener diode 12.The terminal 16 is connected to the line 14 through a capaci tor C7. Thelines 13, 14 are bridged by a d.c. source 19, conveniently in the formof a number of nickelcadmium secondary cells. v

The circuit further includes an N-P-N transistor Q1 having its emitterconnected to the line 14 and its collector connected to the line 13through a resistor R2. The collector and base of the transistor Q1 areinterconnected through a resistor R1, and the collector is furtherconnected through a resistor R3 to the base of an N-P-N transistor Q2,the emitter of which is connected to the line 14 through a resistor R5and the collector of which is connected to the line 13 through aresistor R4. The collector and base of the transistor Q2 areinterconnected through a capacitor C1, and the collector is furtherconnected to the base of a P-N-P transistor Q3, the emitter of which isconnected to the line 13 through a resistor R6 and the collector ofwhich is connected to the base of an N-P-N transistor Q4 having itscollector connected to the line 13 through the resistor R6 and itsemitter connected to the'line 14 through a resistor R7. The emitter ofthe transistor 04 is further connected to the base of an N-P-Ntransistor Q5 having its emitter connected to the line 14, its collectorconnected to the line 13 through a solenoid 21 bridged by a diode D1,and its collector and base interconnected through a capacitor C6. A pairof resistors R14, R13 are connected in series across thecollectoremitter of the transistor Q5, and the junction of the resistorsR14, R13 is connected to the base of the transistor Q2 through a presetresistor 22. The base of the transistor 05 is further connected througha resistor R11 and a thermistor 23 in series to the base of thetransistor Q1.

An input to the base of the transistor Q1 is provided from the terminal16 by way of resistors R9, R10 and a capacitor C2 in series. Thejunction of the resistors R9, R10 is connected to the line 13 through aresistor R16 and to the line 14 through a capacitor C3, which is bridgedby a normally open switch 24 and a resistor R15 in series. The junctionof the resistor R10 and capacitor C2 is connected to the line 14 througha capacitor C4, and as will be explained later, the capacitor C2 can beconnected to the base of the transistor O2 instead of to the base of thetransistor Q1.

The alternator produces an output which is dependent on speed, and thisoutput is passed through the transistor Q6 and its associated componentswhich act in known manner to provide a constant current to the lines 13,and to charge the battery 19. The resistors R9, R10 and capacitors C7,C3, C4 act as a smoothing network, and the smoothed output is passedthrough the capacitor C2 to the base of the transistor Q1, so that asignal appears at the base of the transistor Q1 only when the wheel isaccelerating or decelerating. The Signal will be negative with respectto the line 14 when the wheel is decelerating, but positive with respectto the line 14 when the wheel is accelerating. A signal which ispositive with respect to the line 14 has no effect with the capacitor C2connected to the base of the transistor Q1 as shown, and so accelerationsignals can be ignored.

Assuming that the rail vehicle is not decelerating, and the transistorQ1 is maintained conductive by current flow through resistors R2, R1,and so removes part but not all of the base current from the transistorQ2. Conduction of the transistor Q2 turns on the transistor Q3, which inturn causes conduction of the transistor Q4 which provides base currentto the transistor 05, so that all the transistors are'conducting.However, the circuit values are such that the current flowing throughthe transistor Q5 to the solenoid 21 is insufficient to energiz'e thesolenoid 21.

.When the brakes of the rail vehicle are applied so that the wheeldecelerates, a negative signal having a magnitude dependent on thedeceleration passes through the capacitor C2 and tends to turn thetransistor Q1 off, so that more current can flow through the resistorR3, and the transistors Q2, Q3, Q4 and Q5 all conduct more. The amountby which the transistor Q2 conducts is determined by the value of theresistor 22, which provides an alternative path for current flowingthrough the resistor R3. The value of the resistor 22 is set onmanufacture so that when a predetermined signal passes through thecapacitor C2 representing a condition in which the wheels are close tolocking, then the transistor Q5 will conduct sufficiently to energizethe solenoid 21. The solenoid 21 is connected in the braking system inany convenient manner so that when it is energized it releases thebrakes.

It will be appreciated that the arrangement described actuallyanticipates locking of the wheels, so that in theory the brakes will bereleased actually before the wheel locks. However, in practice there isinevitably a delay between the receipt of the signal through thecapacitor C2, and the release of the brakes by energization of thesolenoid 21. During this delay period, it is possible for the wheels tolock, and if this happens the wheel will of course cease to decelerateso that no further signal will pass through the capacitor C2, and if nosteps were taken the brakes would not be released. The capacitor C1 isprovided to overcome this difficulty. When the transistor Q1 turns off,the capacitor C1 is discharged. In the event that the wheels lock sothat the transistor Q1 turns on again, then the collector of thetransistor Q1 will fall towards the potential of the line 14, soreducing the base current of the transistor Q2 with the resultantpossibility that the solenoid 21 will be de-energized. In thecircumstances the capacitor C1 charges through the base and emitter ofthe transistor Q2, the resistor R5, the resistors R13, R14, the solenoid21 and the resistor R4, so holding the transistor Q2 conductive for apredetermined period of time. As long as the transistor O2 isconducting, the transistors Q3, Q4 and Q5 will also be conducting andthe solenoid will remain energized, and so in this way the arrangementensures that the brakes will be released even if the wheel should lockbefore the actual release takes place.

If it is desired to use the circuit to control acceleration of thewheel, the capacitor C2 is connected to the base of the transistor Q2instead of to the base of the transistor Q1. A negative signal passedthrough the capacitor C2 during deceleration now tends to turn thetransistor Q2 off, but this does not matter because reduction in currentthrough the transistor Q2 will only result in a reduction in currentthrough transistors Q3, Q4, and Q5, and so a reduction in currentthrough the solenoid 21, which in any case was not energized. However,when the wheel is accelerating, apositive signal is applied to the baseof the transistor Q2 tending to cause it to conduct more. At apredetermined acceleration which is chosen by selection of the resistor22 to be just before the wheel is liable to slip, the transistor 02 willconduct sufficiently to cause the transistor O5 to supply sufficientcurrent to the solenoid 21 to energize it. The solenoid, when energized,operates any convenient mechanism for preventing the driver of the railvehicle from increasing the power supplied to the wheel further. Thecapacitor C1 has exactly the same function in this operation as when thewheel is decelerating.

The switch 24 is provided to enable the circuit to be tested. Thus, whenthe switch 24 is closed, it provides a signal through the capacitor C2representing acceleration of the wheel. This signal has no effect, butwhen the switch 24 is open again, it supplies a signal which isequivalent to a deceleration signal, so that the solenoid 21 should bemomentarily energized. It will be noted that the position of the switch24 is such that no separate source is required for testing thearrangement, the power being supplied by the battery 19. Furthermore,the important parts of the circuit will be tested even if the battery 19is partly discharged, and so the risk of the solenoid not operating as aresult of inadequate battery voltage, with'consequential false diagnosisof circuit failure, is minimized. The switch 24 is preferablymagnetically operated and the arrangement is such that normally theswitch is magnetically screened from an adjacent magnet by a ferrousscreen. When carrying out a test, the screen is momentarily moved out ofits normal position, for example by a push button, and so the switchcomes under the influence of the magnet and closes. Releasing the switchbutton then allows the screen to return so that the switch re-opens. Theswitch could, however, be normally closed and opened by a magnet.Obviously many other forms of switch can be used.

The thermistor 23 in the base circuit of the transistor Q1 serves inconjunction with the resistor R11 to compensate for temperature changes.

The entire circuit shown can be fitted within the axle box of the wheel,and forms a convenient selfcontained unit. The self-power arrangement isparticularly useful on vehicles having no power supply, but is alsouseful on vehicles with a power supply, because there are widevariations in. the nominal voltage of the supply in such vehicles, andbetween the voltages used by different railway companies, andself-powered unit permits complete standardization. Difficultiesresulting from interference from other supplies (e.g., fluorescentlamps) are also avoided.

Although it is preferred to use a dc. source in the form of a battery19, the battery can, in certain examples, be replaced by a capacitorwhich acts as the do. source.

It is of course only necessary to provide one unit of the form describedfor each axle on a rail vehicle, even though the axle has two wheels onit. If the axles on a rail vehicle are coupled, as is the case in somevehicles, then of course expense can be saved by fitting a unit to oneonly of the axles. Moreover, even when the axles are not coupled,expense may be saved if desired, by using a single control unit on oneof the axles and releasing the braking part from all the axlessimultaneously. In such an arrangement, signals would be obtained fromall the axles, so that if any one of the wheels started to skid, thebrakes would be released from all the axles.

The capacitor C6 is included to ensure that the negative feedbackapplied by way of R13, 22, R11 and 23 does not produce instability.

Having thus described our invention what we claim as new and desire tosecure by Letters Patent is:

1. Means for controlling the acceleration of a wheel, comprising agenerator driven by the wheel, means for producing an electrical signalhaving a magnitude dependent on the acceleration of the wheel, a dc.control circuit to which said signal is supplied, said control circuitincluding means operable in use to prevent transmission of driving powerto said wheel when the magnitude of said signal reaches apredeterminedvalue, a dc. source which is charged by said generator and provides thesole power to said control circuit, a voltage regulator controlling thecharging of said do. source by said generator, and a delay networkwithin said control circuit for maintaining the circuit in a conditionto prevent supply of power to said wheel in the event that the wheelshould start to slip before said power is released. t *1 t t

1. Means for controlling the acceleration of a wheel, comprising agenerator driven by the wheel, means for producing an electrical signalhaving a magnitude dependent on the acceleration of the wheel, a d.c.control circuit to which said signal is supplied, said control circuitincluding means operable in use to prevent transmission of driving powerto said wheel when the magnitude of said signal reaches a predeterminedvalue, a d.c. source which is charged by said generator and provides thesole power to said control circuit, a voltage regulator controlling thecharging of said d.c. source by said generator, and a delay networkwithin said control circuit for maintaining the circuit in a conditionto prevent supply of power to said wheel in the event that the wheelshould start to slip before said power is released.